Abstract
Multi-slice perfusion-based functional magnetic resonance imaging (p-fMRI) is demonstrated with a color–word Stroop task as an established cognitive paradigm. Continuous arterial spin labeling (CASL) of the blood in the left common carotid artery was applied for all repetitions of the functional run in a quasi-continuous fashion, i.e., it was interrupted only during image acquisition. For comparison, blood oxygen level dependent (BOLD) contrast was detected using conventional gradient-recalled echo (GE) echo planar imaging (EPI). Positive activations in BOLD imaging appeared in p-fMRI as negative signal changes corresponding to an enhanced transport of inverted water spins into the region of interest, i.e., increased cerebral blood flow (CBF). Regional differences between the localization of activations and the sensitivity of p-fMRI and BOLD-fMRI were observed as, for example, in the inferior frontal sulcus and in the intraparietal sulcus. Quantification of CBF changes during cognitive task activation was performed on a multi-subject basis and yielded CBF increases of the order of 20–30%.
Highlights
In the last decade, perfusion imaging using magnetic resonance imaging (MRI) techniques with water as an endogenous tracer has been a topic of growing research
In order to include the effect of changing transit time, the quantity A has to be estimated. For this purpose, we use data from a recent finger-tapping study (Hernandez-Garcia et al, 2004), which reported an arterial transit-time change of 150 ms and a signal increase of 83%, both averaged over five subjects
CBF increases during the Stroop task of an order of 20 – 30% were obtained
Summary
Perfusion imaging using magnetic resonance imaging (MRI) techniques with water as an endogenous tracer has been a topic of growing research. The perfusion contrast created by magnetically labeling of the blood or the tissue was employed for mapping task-related brain activity (Edelman et al, 1994; Kwong et al, 1992). Due to its higher sensitivity, the blood oxygen level dependent (BOLD) contrast became the standard tool for functional MRI (fMRI). Despite this fact, interest in perfusion-based fMRI (p-fMRI) remained high. Techniques were developed to increase the number of slices, to reduce the transit-time sensitivity, and to improve the time resolution in p-fMRI (Alsop and Detre, 1998; Calamante et al, 1999; Pekar et al, 1996; Zhang et al, 1995). Except for a single-slice study employing a workingmemory task (Ye et al, 1998), all published studies were limited to primary cortical areas, such as the visual or the motor cortex
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